The present invention relates to a data converter apparatus and method and also to a database-to-object inspection system including such a data converter. The invention is particularly useful for, but is not limited to, optically inspecting masks utilized in constructing integrated circuit reticles and wafers and/or the integrated circuit reticles and wafers constructed with such masks. The invention is therefore described below particularly with respect to this application.
Database-to-object inspection systems as used for inspecting masks, or the chips or wafers constructed with such masks, include an optical inspection system for inspecting the object and for outputting a series of pixels corresponding to the inspected surface, and a database containing design data corresponding to a reference, or defectless, object. The object data output from the optical inspection system is compared with the design data in the database, and mismatches or discrepancies are outputted in the form of a list of defects.
Mask inspection involves, normally, successively scanning e.g. vertical slices of the inspected mask surface, where each slice typically extends over a narrow strip (say 1024 to 2048 pixels). The scanning of a slice results in a stream of pixels that is compared to a similar stream of pixels that originates from a corresponding slice of a reference defectless object. As explained before, any discrepancies are recorded in a list of defects.
By following this approach, the design data from the database must be fed to the comparator at approximately the same rate as the object data from the inspection system; otherwise, the inspection system will have to slow down, causing a reduction in inspection rate and a lowering of the machine throughput.
The design data is normally stored in a number of design formats, such as GDS II, JEOL, Hitachi, MEBES. However, these data after having been combined into a single file and converted to output format, are very large, approaching disc volume, and their density (features per area) is very high. Handling data files of such sizes and densities involves serious problems in disc space, computer memory, communication transfer rate, computation time, etc., needed to convert from the design format to the machine""s internal format. These problems are made even more severe by the continuous increase and complexity of the data in the new technologies.
For these reasons, the design data is converted off-line, and before the inspection starts, into a compact format comprised of a plurality of repeating, predefined units, including basic geometric figures (hereinafter called BGFs), cells and/or arrays thereof, and their locations in the pattern. A common BGF is a trapezoid, but other BGFs may be used, such as polygons, lines, etc. Thus, the compact format, sometimes called a Hierarchical format or HIF, needs to define each different BGF only once, and to specify each location of each so-defined BGF, thereby enabling the pattern to be described with considerably less data.
Accordingly, in order to exploit the data that originate from the defectless design data as a basis for comparison, a preliminary format conversion step should be effected. More specifically, the trapezoid data in a slice in the reference defectless design data (represented in HIF format) must be converted into a corresponding stream of pixels that is organized in the same fashion as the stream of pixels in a scanned slice of the inspected mask, to thereby facilitate the specified comparison.
Generally speaking, this preliminary conversion step involves dealing with a very large volume of data (including a huge amount of BGF data) that should be converted. This necessitates a relatively prolonged computation time in order to convert the BGF representation from the input format (HIF) into the stream of pixels as explained above. The time required for these computations may adversely affect the performance of the converter to such an extent which it may no longer be able to meet real-time requirements that are dictated by the scanning rate of the inspected object.
In light of the above identified problems, there is a need in the art for a data converter apparatus and method for converting design data stored in a compact format into expanded real-time data so that the design data is present to the comparator in the inspection system essentially at the same rate as the inspection data.
According to one aspect of the present invention, there is provided a data converter apparatus for converting in essentially real time data stored in an input compact format into an output expanded real time format, the data including a plurality of groups and instances thereof, each group including a plurality of basic geometric figures (BGF); the data converter comprising:
first processor adapted to receiving the data stored in the compact format, selecting data relating to a pre-defined division, which division includes a plurality of groups, dividing each group into at least one bin, determining the number of instances of each different bin in a respective division, converting the format of the data of the plurality of BGFs in each different bin into an output related format, outputting a list of different bins and the location of the bins in the respective division;
a partial expander adapted to receiving, expanding and sorting said list of bins in each respective division, according to scan order; and
a final expander adapted to sub-dividing, according to scan order, each division into a plurality of sub-divisions, processing and allocating each BGF in a respective bin into a sub-division according to the location of the respective BGF in the bin and the location thereof in the sub division, generating a sub-division data stream representative of the plurality of BGFs in a respective sub division, and combining said sub-division data streams into one data stream in said output expanded real time format, which data stream is representative of the plurality of BGFs in the respective division.
The invention further provides for data converter apparatus for converting in essentially real time data stored in an input compact format into an output expanded real time format, the data including a plurality of groups and repetitions thereof, each group including a plurality of basic geometric figures (BGF); the data converter comprising:
a processor adapted to selecting data relating to a predetermined division, dividing and processing said data into consecutive bins according to scan order, which bins have structural correspondence to the input format;
sub dividing the respective division into sub-divisions having structural correspondence to the output format;
processing and allocating the BGFs in the bins to subdivisions to thereby producing a division data stream in said output expended real time format.
Still further, the invention provides for a database-to-object inspection system, including:
an optical inspection system optically inspecting a surface of an object and outputting a series of pixels corresponding to the surface thereof;
a database containing design data of the object, which design data is stored in an input compact format;
data converter apparatus of the kind specified, adapted to convert in essentially real time the data stored in the input compact format into an output expanded real time format;
a comparator comparing in real time the series of pixels outputted by the optical inspection system with a series of pixels in said real time expanded format outputted by said converter apparatus.
The invention further provides for a method for converting in essentially real time data stored in an input compact format into an output expanded real time format, the data including a plurality of groups and instances thereof, each group including a plurality of basic geometric figures (BGF); the method comprising the following steps:
(a) receiving the data stored in the compact format,
(b) selecting data relating to a pre-defined division, which division includes a plurality of groups,
(c) dividing each group into at least one bin,
(d) determining the number of instances of each different bin in a respective division,
(e) converting the format of the data of the plurality of BGFs in each different bin into an output related format,
(f) outputting a list of different bins and the location of the bins in the respective division;
(g) partially expanding said list of bins in each respective division, according to scan order;
(h) sub-dividing, according to scan order, each division into a plurality of sub-divisions,
(i) processing and allocating each BGF in a respective bin into a sub-division according to the location of the respective BGF in the bin and the location thereof in the sub division,
(j) generating a sub-division data stream representative of the plurality of BGFs in a respective sub division; and
(k) combining said sub-division data streams into one data stream in said output expanded real time format, which data stream is representative of the plurality of BGFs in the respective division.
The invention still provides for a method for converting in essentially real time data stored in an input compact format into an output expanded real time format, the data including a plurality of groups and repetitions thereof, each group including a plurality of basic geometric figures (BGF); the method comprising the following steps:
(a) selecting data relating to a predetermined division,
(b) dividing and processing said data into consecutive bins according to scan order, which bins have structural correspondence to the input format;
(c) sub dividing the respective division into sub-divisions having structural correspondence to the output format;
(d) processing and allocating the BGFs in the bins to subdivisions to thereby producing a division data stream in said output expended real time format.
Still further, the invention provides for a method for optically inspecting a surface of an object, comprising:
storing in a database design data of the object in a compact format;
converting the database design data stored in said compact format into a stream of pixels in an expanded real time format, according to the specified method;
optically inspecting said surface and producing a stream of pixels corresponding to the inspected surface; and
comparing in real time the stream of pixels corresponding to the inspected surface with the stream of pixels in said real time expanded format.
As indicated above, the invention is particularly useful in a database-to-object inspection system. In such systems, the predefined divisions represent e.g. slices of the object (e.g., a mask representing a frame or layer of an IC chip or wafer, or the chip or wafer itself) having a plurality of patterns, and the subdivisions are e.g. equally divided windows of the respective object.
As will be described more particularly below, a data converter apparatus constructed in accordance with the foregoing features particularly when used in a database-to-object inspection system, provide a number of important advantages, including the following: (1) it maintains the original database hierarchy, and thereby keeps the data files very compact, of similar size (or smaller) than the original database of compact format; (2) it enables the compaction to be retained far within the data path, thereby reducing the limitations of memory and communication transfer rate; (3) it enables the use of hardware and software which are scaleable, permitting duplicate components to be added where necessary to handle more complex and/or dense data without substantially slowing down the overall inspection operation; and (4) it permits dynamic slowdown to be performed when a limitation (memory, transfer rate, etc.) is reached during the inspection process, by changing the width of the slice, while retaining the maximum scanning rate.
Further features and advantages of the invention will be apparent from the description below.
The invention is herein described, by way of example only, with reference to the accompanying drawings, wherein:
FIG. 1 illustrates an example of an optical inspection system in accordance with the present invention;
FIG. 2 illustrates various possible levels of the hierarchial compact format of the design data in the inspection system of FIG. 1;
FIG. 3 illustrates an example of a detailed structure of a typical pattern in the hierarchial compact format of FIG. 2;
FIG. 4 illustrates an example of a frame containing a plurality of patterns and a slice which covers a portion of each one of a vertically extending patterns;
FIG. 5A illustrates a pattern A, of the kind depicted in FIG. 4, partitioned into three consecutive bins;
FIG. 5B illustrates the slice of FIG. 4 and the respective locations of the bins and windows in the slice;
FIG. 5C illustrates an inject list of the bins that are depicted in FIG. 5A;
FIGS. 6A-6E illustrate a plurality of trapezoid sequences that are subjected to clipping in the X and Y coordinate;
FIG. 7 is an overall block diagram of one form of data converter apparatus in accordance with the present invention;
FIG. 8 is a block diagram illustrating an ITPP (Inspection Time Pre-Processor) in the data converter apparatus of FIG. 7;
FIG. 9 illustrates an example of a flow chart of a typical sequence of operation in an optical inspection system of FIG. 1;
FIG. 10 is a block diagram illustrating one form of spanner for performing the final expansion in the data converter apparatus of FIG. 7;
FIG. 11 is a block diagram illustrating one form of Pre-line system in the spanner of FIG. 10;
FIG. 12 is a block diagram illustrating one form of Line Machine in the spanner of FIG. 10;
FIG. 13 is a block diagram illustrating one form of Fill Machine in the spanner of FIG. 10;
FIG. 14 is a block diagram illustrating one form of Fill-Logic circuit in the spanner of FIG. 10;
FIG. 15 illustrates a preferred implementation of data converter apparatus in accordance with the present invention; and
FIG. 16 illustrates an example of a time sequence for performing the various operations in the data converter apparatus of FIG. 15.